The present invention relates to fiber optic networks, and more particularly to wavelength division multiplexers, wavelength division de-multiplexers, optical isolators and optical circulators utilized in fiber optic networks carrying wavelength division multiplexed information signals.
Fiber optic communication systems are becoming increasingly popular for data transmission due to their high speed and high data capacity capabilities. Wavelength division multiplexing is used in such fiber optic communication systems to transfer a relatively large amount of data at a high speed. In wavelength division multiplexing, multiple information-carrying signals, each signal comprising light of a specific restricted wavelength range, may be transmitted along the same optical fiber.
In this specification, these individual information-carrying lights are referred to as either xe2x80x9csignalsxe2x80x9d or xe2x80x9cchannels.xe2x80x9d The totality of multiple combined signals in a wavelength-division multiplexed optical fiber, optical line or optical system, wherein each signal is of a different wavelength range, is herein referred to as a xe2x80x9ccomposite optical signal.xe2x80x9dThe term xe2x80x9cwavelength,xe2x80x9d denoted by the Greek letter xcex (lambda) is used herein in two senses. In the first usage, this term is used according to its common meaning to refer to the actual physical length comprising one full period of electromagnetic oscillation of a light ray or light beam. In its second usage, the term xe2x80x9cwavelengthxe2x80x9d is used synonymously with the terms xe2x80x9csignalxe2x80x9d or xe2x80x9cchannel.xe2x80x9d Although each information-carrying channel actually comprises light of a certain range of physical wavelengths, for simplicity, a single channel is referred to as a single wavelength, xcex, and a plurality of n such channels are referred to as xe2x80x9cn wavelengthsxe2x80x9d denoted xcex1-xcexn. Used in this sense, the term xe2x80x9cwavelengthxe2x80x9d may be understood to refer to xe2x80x9cthe channel nominally comprised of light of a range of physical wavelengths centered at the particular wavelength, xcex.xe2x80x9d
A crucial feature of fiber optic networks is the separation of the composite optical signal into its component wavelengths or channels, typically by a wavelength division de-multiplexer. This separation must occur to allow for the exchange of signals between loops within optical communications networks. The exchange typically occurs at connector points, or points where two or more loops intersect for the purpose of exchanging wavelengths. Conventional methods utilized by wavelength division de-multiplexers in separating a composite optical signal into its component channels include the use of filters and fiber gratings as separators. A xe2x80x9cseparatorxe2x80x9d or xe2x80x9cchannel separatorxe2x80x9d, as used in this specification, is an integrated collection of optical components functioning as a unit which separates one or more channels of a composite optical signal from one another or else combines separate channels from separate inputs into a composite optical signal.
Additional important components of wavelength division multiplexed optical communication systems are optical comb filters, optical isolators and optical circulators. Optical comb filters supplement channel separators so as to improve the separation of channels from one another. Optical isolators prevent inadvertently reflected signals from propagating through the communications system opposite to their intended direction. Optical circulators are crucial components for permitting bi-directional communications. At present, there does not exist any single apparatus that combines the functionality of a channel separator with that of an isolator, a circulator, or a comb filter.
Accordingly, there exists a need for a multi-functional separator which is easier to align. The multi-functional separator should easily incorporate additional isolator, circulator and comb-filter functionalities. The present invention addresses such a need.
The present invention provides a multi-functional optical device. The optical device includes: a first birefringent plate; a first set of optical rotators optically coupled to the first birefringent plate, the first set of optical rotators comprising a first non-reciprocal optical rotator (NRR) and a first reciprocal optical rotator (RR); a second birefringent plate optically coupled to the first set of optical rotators at a side opposite to the first birefringent plate; and a first non-linear interferometer (NLI) optically coupled to the second birefringent plate at a side opposite to the first set of optical rotators. Provision of additional reflectors and/or optical ports leads to additional optical isolator and optical circulator functionality. Provision of additional non-linear interferometers and/or optical ports leads to additional comb filtering and or two-stage channel separation capabilities. The optical device in accordance with the present provides greater ease in alignment and functional versatility than prior-art channel separators.